Android lifecycle 实战及使用进阶

前言

Android Architecture Components 的，前面我们已经讲解了 lifecycle， LiveData 的使用及原理，今天，让我们一起赖看看 lifecycle 在项目中的实战。主要讲解两点

LifecycleHandler 的封装
MVP 中引入 lifecycle，可以自行监听 activity 生命周期变化

LifecycleHandle 的封装

我们平时在使用 handler 的时候，在 activity onDestroy 的时候，需要手动取 removeMessage 或者 removeCallBack，不然的话，很容易发生内存泄漏。

@Override
protected void onDestroy() {
    super.onDestroy();
    mHandler.removeCallbacksAndMessages(null);
}

这对我们开发者来说，很明显是一个重复的动作。我们一起通过 lifecycle 来减少这种重复性的动作，让其内部自己释放。

核心原理其实很简单，内部监听 activity 生命周期的变化，在 onDestroy 的时候移除 message 和 callback。

public class LifecycleHandler extends Handler implements FullLifecycleObserver {


    private LifecycleOwner mLifecycleOwner;

    public LifecycleHandler(LifecycleOwner lifecycleOwner) {
        mLifecycleOwner = lifecycleOwner;
        addObserver();
    }

    public LifecycleHandler(LifecycleOwner lifecycleOwner, Callback callback) {
        super(callback);
        mLifecycleOwner = lifecycleOwner;
        addObserver();
    }

    public LifecycleHandler(LifecycleOwner lifecycleOwner, Looper looper) {
        super(looper);
        mLifecycleOwner = lifecycleOwner;
        addObserver();
    }

    public LifecycleHandler(LifecycleOwner lifecycleOwner, Looper looper, Callback callback) {
        super(looper, callback);
        mLifecycleOwner = lifecycleOwner;
        addObserver();
    }

    private void addObserver() {
        if (mLifecycleOwner != null) {
            mLifecycleOwner.getLifecycle().addObserver(new FullLifecycleObserverAstrong textdapter(mLifecycleOwner, this));
        }
    }


    @Override
    public void onCreate(LifecycleOwner owner) {

    }

    @Override
    public void onStart(LifecycleOwner owner) {

    }

    @Override
    public void onResume(LifecycleOwner owner) {

    }

    @Override
    public void onPause(LifecycleOwner owner) {

    }

    @Override
    public void onStop(LifecycleOwner owner) {

    }

    @Override
    public void onDestroy(LifecycleOwner owner) {
        removeCallbacksAndMessages(null);
    }
}

我们来看一下这一行代码

mLifecycleOwner.getLifecycle().addObserver(new FullLifecycleObserverAdapter(mLifecycleOwner, this));

FullLifecycleObserverAdapter 是什么呢？

FullLifecycleObserverAdapter

public class FullLifecycleObserverAdapter implements LifecycleObserver {

    private final FullLifecycleObserver mObserver;

    private static final String TAG = "FullLifecycleObserverAd";
    private final LifecycleOwner mLifecycleOwner;

    FullLifecycleObserverAdapter(LifecycleOwner lifecycleOwner, FullLifecycleObserver observer) {
        mLifecycleOwner = lifecycleOwner;
        mObserver = observer;
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_CREATE)
    public void onCreate() {
        Log.i(TAG, "onCreate: ");
        mObserver.onCreate(mLifecycleOwner);
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_START)
    public void onStart() {
        Log.i(TAG, "onStart: ");
        mObserver.onStart(mLifecycleOwner);
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
    public void onResume() {
        Log.i(TAG, "onResume: ");
        mObserver.onResume(mLifecycleOwner);
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)
    public void onPause() {
        Log.i(TAG, "onPause: ");
        mObserver.onPause(mLifecycleOwner);
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_STOP)
    public void onStop() {
        Log.i(TAG, "onStop: ");
        mObserver.onStop(mLifecycleOwner);
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
    public void onDestroy() {
        Log.i(TAG, "onDestroy: ");
        mObserver.onDestroy(mLifecycleOwner);
    }

}

FullLifecycleObserver

public interface FullLifecycleObserver extends LifecycleObserver {

    void onCreate(LifecycleOwner owner);

    void onStart(LifecycleOwner owner);

    void onResume(LifecycleOwner owner);

    void onPause(LifecycleOwner owner);

    void onStop(LifecycleOwner owner);

    void onDestroy(LifecycleOwner owner);
}

FullLifecycleObserver 是我们自己自定义的一个接口，继承 LifecycleObserver，各个方法一一对应 activity 的生命周期。

FullLifecycleObserverAdapter 实现了 LifecycleObserver，使用了 @OnLifecycleEvent 注解，在 activity 生命周期变化的时候会回调相应的方法，我们再在里面回调 observer 的 onCreate， onStart 等方法，这有点类似代理模式。调用关系总结如下：

enter description here

以后想观察 lifecycle 生命周期变化的话，只需要 mLifecycleOwner.getLifecycle().addObserver(new FullLifecycleObserverAdapter(mLifecycleOwner, this)); 这一行代码即可

有人可能会这样问了，为什么要这样设计呢

加 FullLifecycleObserver 这个接口，主要是为了跟 activity 的生命周期一一对应。

LifecyclePresenter 的封装

public class LifecyclePresenter implements IPresenter, FullLifecycleObserver {

    private static final String TAG = "BasePresenter";

    private final LifecycleOwner mLifecycleOwner;

    public LifecyclePresenter(LifecycleOwner lifecycleOwner) {
        mLifecycleOwner = lifecycleOwner;
        mLifecycleOwner.getLifecycle().addObserver(new FullLifecycleObserverAdapter(lifecycleOwner, this));
    }

    @Override
    public void onCreate(LifecycleOwner owner) {
        Log.i(TAG, "onCreate: owner = " + owner);
    }

    @Override
    public void onStart(LifecycleOwner owner) {
        Log.i(TAG, "onStart: owner = " + owner);
    }

    @Override
    public void onResume(LifecycleOwner owner) {
        Log.i(TAG, "onResume: owner = " + owner);
    }

    @Override
    public void onPause(LifecycleOwner owner) {
        Log.i(TAG, "onPause: owner = " + owner);
    }

    @Override
    public void onStop(LifecycleOwner owner) {
        Log.i(TAG, "onStop: owner = " + owner);
    }

    @Override
    public void onDestroy(LifecycleOwner owner) {
        Log.i(TAG, "onDestroy: owner = " + owner);
    }
}

Android 技术人，一位不羁的码农。

Android 技术人